Graphene transistor gated by charges through a nanopore for bio-molecular sensing and DNA sequencing

ABSTRACT

A technique for a nanodevice is provided. A reservoir is separated into two parts by a membrane. A nanopore is formed through the membrane, and the nanopore connects the two parts of the reservoir. The nanopore and the two parts of the reservoir are filled with ionic buffer. The membrane includes a graphene layer and insulating layers. The graphene layer is wired to first and second metal pads to form a graphene transistor in which transistor current flowing through the graphene transistor is modulated by charges or dipoles passing through the nanopore.

DOMESTIC PRIORITY

This is a continuation of U.S. patent application Ser. No. 13/448,509filed Apr. 17, 2012, the contents of which are incorporated in theirentirety by reference herein.

BACKGROUND

The present invention relates generally to identifying anddifferentiating molecules, and more specifically, to identifying anddifferentiating molecules using a graphene nanopore transistor.

Nanopore sequencing is a method for determining the order in whichnucleotides occur on a strand of deoxyribonucleic acid (DNA). A nanopore(also referred to a pore, nanochannel, hole, etc.) can be a small holein the order of several nanometers in internal diameter. The theorybehind nanopore sequencing is about what occurs when the nanopore isimmersed in a conducting fluid and an electric potential (voltage) isapplied across the nanopore. Under these conditions, a slight electriccurrent due to conduction of ions through the nanopore can be measured,and the amount of current is very sensitive to the size and shape of thenanopore. If single bases or strands of DNA pass (or part of the DNAmolecule passes) through the nanopore, this can create a change in themagnitude of the current through the nanopore. Other electrical oroptical sensors can also be positioned around the nanopore so that DNAbases can be differentiated while the DNA passes through the nanopore.

The DNA can be driven through the nanopore by using various methods. Forexample, an electric field might attract the DNA towards the nanopore,and it might eventually pass through the nanopore. The scale of thenanopore can have the effect that the DNA may be forced through the holeas a long string, one base at a time, like thread through the eye of aneedle. Recently, there has been growing interest in applying nanoporesas sensors for rapid analysis of biomolecules such as deoxyribonucleicacid (DNA), ribonucleic acid (RNA), protein, etc. Special emphasis hasbeen given to applications of nanopores for DNA sequencing, as thistechnology holds the promise to reduce the cost of sequencing below$1000/human genome. Two issues in nanopore DNA sequencing arecontrolling the translocation of DNA through the nanopore anddifferencing individual DNA bases.

SUMMARY

According to an embodiment, a method for electrically differentiatingDNA nucleobases and/or identifying biomolecules is provided. The methodincludes configuring a reservoir separated into two parts by a membrane,and configuring a nanopore formed through the membrane. The nanoporeconnects the two parts of the reservoir. The method includes filling thenanopore and the two parts of the reservoir with ionic buffer. Themembrane includes a graphene layer and insulating layers. The graphenelayer is wired to first and second metal pads to form a graphenetransistor in which transistor current flowing through the graphenetransistor is modulated by charges and/or dipoles passing through thenanopore.

According to an embodiment, a method for electrically differentiatingDNA nucleobases and/or identifying biomolecules. The method includesconfiguring a reservoir separated into two parts by a membrane, andconfiguring a nanopore formed through the membrane. The nanoporeconnects the two parts of the reservoir. The method also includesfilling the nanopore and the two parts of the reservoir with ionicbuffer. The membrane includes a graphene layer and insulating layers.The graphene layer is wired to first and second metal pads to form agraphene transistor in which transistor current flowing through thegraphene transistor is modulated by charges and/or dipoles passingthrough the nanopore. The charges and/or dipoles correspond to at leastone of a nucleobase and a biomolecule. The nanopore is coated with anorganic layer configured to at least one of interact with the nucleobasedifferently than other nucleobases and/or interact with the biomoleculedifferently than other biomolecules.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention. For a better understanding of the invention with advantagesand features, refer to the description and to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 illustrates a fabrication process of a cross-section graphenenanopore transistor device according to an embodiment.

FIG. 2A shows a top view of the graphene nanopore transistor device,illustrating the geometry of the buried graphene layer according to anembodiment.

FIG. 2B shows a top view of the graphene nanopore transistor device,illustrating the geometry of the buried graphene layer according to anembodiment.

FIG. 2C shows a top view of the graphene nanopore transistor device,illustrating the geometry of the buried graphene layer according to anembodiment.

FIG. 3 is a setup of the graphene nanopore transistor device for DNAand/or RNA sequencing according to an embodiment.

FIG. 4 is a setup of the graphene nanopore transistor device forbiomolecule sensing according to an embodiment.

FIG. 5 shows a setup of the graphene nanopore transistor device forbiomolecule sensing according to an embodiment.

FIG. 6 illustrates a graph of a transistor current pulse according to anembodiment.

FIG. 7 illustrates a graph of an ionic current pulse according to anembodiment.

FIG. 8 is a flow chart illustrating a method for differentiating andidentifying bases and biomolecules in a nanopore according to anembodiment.

FIG. 9 is a flow chart illustrating a method for differentiating andidentifying bases and biomolecules in a nanopore according to anembodiment.

FIG. 10 illustrates an example of a computer having capabilities, whichmay be included in and/or combined with embodiments.

DETAILED DESCRIPTION

Field effect transistor sensors have been demonstrated for sensingbiomolecules, and are especially suitable for reducing the requiredamount of reagents by leveraging their high sensitivity. However, singlemolecule accuracy and high spatial resolution of, e.g., 0.7 nm(nanometers) for DNA sequencing has not yet been demonstrated using thisapproach.

Embodiments propose the use of a graphene transistor on a freestandingmembrane with a nanopore passing through it. Single molecules can bedriven through the nanopore one by one, and as they go through, eachindividual molecule can modulate the current through the graphenetransistor. This configuration allows molecular detection with singlemolecule accuracy. As the graphene layer can be as thin as 0.335 nm(nanometers), the spatial resolution of this approach can be 0.335 nm,which is enough for DNA sequencing purpose.

FIG. 1 illustrates a fabrication process of a cross-section nanoporegraphene transistor device 100, with detailed material layers andprocess flow (figure not to scale) according to an embodiment. Thegraphene nanopore transistor device 100 is a chip.

The graphene nanopore transistor device 100 includes a substrate 101which may be a silicon (Si) substrate. A layer 102 is an insulationlayer which may be LPCVD (low pressure chemical vapor deposition) Si₃N₄(around 30 nm in thickness). A layer 103 is an insulation layer whichmay be 250 nm thick Si₃N₄, including 30 nm LPCVD Si₃N₄ and 220 nm PECVD(plasma enhanced chemical vapor deposition) Si₃N₄.

To form the graphene layer 104, thin films of graphene can be formed byCVD (chemical vapor deposition) growth on metal, by exfoliation of bulkgraphite, or by epitaxial grown on SiC (silicon carbide) by hightemperature decomposition of its surface and sublimation of Si. Amongthese methods, graphene grown on copper can produce the largest filmarea (up to 30 inches in width). The underlying copper can be etchedaway by copper etchant and transferred to targeting substrate by usingthermal release tape, PMMA (polymethyl methacrylate), or PDMS(polydimethylsiloxane). In this application, the graphene film/layer 104can be transferred onto LPCVD Si₃N₄ layer 102 and be patterned throughphotolithography or ebeam lithography followed by reactive ion etching(RIE) based on O₂ plasma. The photo/e-beam resist can be cleaned byAcetone without damaging the graphene layer 104. The reason to patternthe graphene layer 104 is to make it smaller than the followingmetal/electrically conductive pads 105 a and 105 b, which can bedeposited by ebeam evaporation with patterned photoresist on top and canbe patterned by a metal lifting off process. The metal pads 105 a and105 b can be a stack of Ti/Pd/Au (titanium/palladium/gold). As the metalpads 105 a and 105 b partially covers the top of both the graphene layer104 and the substrate 101, this (covering) will fix (prevent) thegraphene layer 104 from slipping during any following process.Insulation (passivation) layer 106 (made of thin Si₃N₄ (around 30 nm),200 nm SiO₂, and 200 nm Si₃N₄) is deposited on top of the metal pads 105a and 105 b.

A window area 150 is opened on layer 103 through photolithography andRIE, after which KOH (potassium hydroxide) or TMAH (tetramethylammoniumhydroxide) can be used to etch through the Si substrate 101 at thewindow area 150, to make a free-standing membrane 155 on the front side.

Vias (holes) 107 and 108 are etched through insulation layer 106. Theetching stops on the metal pads 105 a and 105 b to provide access to themetal pads 105 a and 105 b via external electrical probes (which includewires as shown in FIGS. 3, 4, and 5). Via (hole) 109 is partially etchedthrough insulation layer 106 (etching the 200 nm SiO₂ and 200 nm Si₃N₄layers (of layer 106) and then stopping on 30 nm thick Si₃N₄ layer (oflayer 106), which is employed to protect the graphene layer 104underneath). Nanopore 110 through the stacked layers 106, 104, and 102with sizes ranging from 0.5 nm to 100 nm can be made via TEM(transmission electron microscopy) drilling or other techniques.

FIG. 2A shows an implementation of the top view of the graphene nanoporetransistor device 100, illustrating the geometry of the buried graphenelayer 104. The graphene layer 104 has a narrow part (neck) around thelocation where the nanopore 110 is made so that charges on biomoleculesand/or nucleobases will largely affect the transistor current throughthe graphene nanopore transistor device 100. The nanopore 110 is shownat the center of the narrowest part of the graphene layer 104. Thenanopore 110 can also be offset and/or even out of the edge of thegraphene layer 104, as illustrated in FIG. 2B and FIG. 2C.

FIG. 2B show another implementation of the top view of the graphenenanopore transistor device 100, illustrating the geometry of the buriedgraphene layer 104 in which the nanopore 110 is offset on only part ofthe graphene layer 104. The circumference of the nanopore 110 is notcompletely through the graphene layer 104, while the circumference ofthe nanopore 110 fully continues through layers 106 and 102.

FIG. 2C shows another implementation of the top view of the graphenenanopore transistor device 100, illustrating the geometry of the buriedgraphene layer 104 in which the nanopore 110 is off the edge of thegraphene layer 104 without touching the graphene layer 104. Thecircumference of the nanopore 110 is not (at all) through the graphenelayer 104 (but is proximate or nearly adjacent to the graphene layer 104with distance of about a couple nanometers to a couple of micrometers),while the circumference of the nanopore 110 fully continues throughlayers 106 and 102.

FIG. 3 shows a setup 300 of the graphene nanopore transistor device 100for DNA (or RNA) sequencing according to an exemplary embodiment. FIG. 3shows a cross-sectional view of the graphene nanopore transistor device100. Elements 101-110 in FIG. 3 are the same as described FIG. 1, andelements 150 and 155 are not repeated in FIG. 3 so as not to overlycomplicate FIG. 3. Top reservoir 211 and bottom reservoir 212 (whichcould be any orientation including one side and another side) are sealedto each side of the (chip) graphene nanopore transistor device 100.

Reservoirs 211 and 212, and the nanopore 110 are then filled with ionicbuffer 213. The ionic buffer 213 is an electrical conducting fluid ofions. A single strand DNA molecule 217 (with bases 218 illustrated asovals and the backbone 205 illustrated as a solid line) is loaded intothe nanopore 110 by an electrical voltage bias of a voltage source 216,applied across the nanopore 110 via two electrochemical electrodes 214and 215, which were dipped in the ionic buffer 213 of the two reservoirs212 and 211.

The DNA molecule 217 has charges on its molecular backbone 205 as wellas different dipole moments for each of its DNA bases 218. When DNAmolecule 217 is in ionic buffer, the free mobile ions in the ionicbuffer 213 will concentrate around the charged DNA molecule 217 toelectrically screen any charge on the DNA. The ions that screen thecharged DNA are called counter-ions. As the counter ions are underthermal agitation, so the charged ions will spread out with a lengthscale, called Debye length, instead of tightly wrapping the DNA molecule217. When the ionic concentration of ionic buffer 213 is low enough thatthe Debye length is comparable to or larger than the radius of nanopore110, and the electrical field from both the charge on the backbone 205and dipole moment on bases 218 will be largely unscreened fromcounter-ions and be interacting with the graphene layer 104.

Dipole moment (μ) is the measure of net molecular polarity, which is themagnitude of the charge Q at either end of the molecular dipole timesthe distance r between the charges, which is shown by the equationμ=Q×r. Dipole moments tell us about the charge separation in a molecule.The larger the difference in electronegativities of bonded atoms, thelarger the dipole moment.

Voltage (DC or AC) by voltage source 219 is applied on the two ends ofthe graphene layer 104 via two the metal pads 105 a and 105 b at holes107 and 108 respectively, and current measured by ammeter 220 will bemodulated by the charges (of each base 218) passing through the nanopore110. In this way, different DNA bases 218 (with different dipolemoments) will be able to modulate transistor current measured by theammeter 220 and can be differentiated based on the transistor currentsignal measured by ammeter 220 for respective bases 218 that passthrough the nanopore 110 at the graphene layer 104. Since the graphenelayer 104 can be as thin as 0.335 nm (smaller than base pair distance0.7 nm (which is the distance from one base 218 to the next base 218) ofa stretched single strand DNA), this approach has enough spatialresolution to detect individual bases 218.

The baseline transistor current can be measured by the ammeter 220 whenno base 218 is present in the nanopore 110. For example, the transistorcurrent flow (measured by the ammeter 220) travels from the voltagesource 219, through the metal pad 105 a via hole 107, through one sideof the graphene layer 104 then directly to the other side (via thefree-standing membrane 155) of the graphene layer 104, and out throughthe metal pad 105 b via the hole 108 to be measured by ammeter 220 (notethat as seen in FIGS. 2A-2C, the graphene layer 104 is continuous fromone side to the other side except there is hole (nanopore 110) whichdoes not completely cut/sever the graphene layer 104 into two parts).

The base 218 can be identified/sequenced by the characteristics of thetransistor current pulse triggered due to the presence of the base 218inside the nanopore 110, such as, for example, the magnitude and thetime duration of the transistor current pulse (the time it takes the DNAbase to pass through the nanopore) as expected for the given base 218.When the base 218 is present inside the nanopore 110, the presence ofthis particular base 218 causes the transistor current to modulate(i.e., change). The transistor current flow (e.g., measured by theammeter 220 when the base 218 is inside the nanopore 110) travels fromthe voltage source 219, through the metal layer 105 a via hole 107,through one side of the graphene layer 104 to be modulated by the base218 in the nanopore 110, to the other side (via the free-standingmembrane 155) of the graphene layer 104, and out the metal layer 105 bvia the hole 108. FIG. 6 illustrates a graph 600 of the transistorcurrent pulse measured by ammeter 220 (which can be graphed via asoftware application 1060 in FIG. 10) as discussed herein according toan embodiment. This is just one example that may be displayed on thedisplay (input/output device 1070) of a computer 1000 via the softwareapplication 1060. The graph 600 shows the magnitude/amplitude (e.g., innanoamps) of the transistor current pulse height (relative to thebaseline level of transistor current when there is no DNA (base 218)and/or molecules (e.g., biomolecule 221, 222, 223, 224 in FIGS. 4 and 5)inside the nanopore 110) on the y-axis and shows the time duration (t)of the transistor current pulse on the x-axis. For each respectivebiomolecule 221, 222, 223, 224 and/or each respective base 218, acorresponding transistor current trace (of its transistor current pulsemeasured when inside the nanopore 110) is graphed with a time duration(t) and magnitude as seen in FIG. 6. For example, the base 218 (and/orbiomolecule 221-224) in the nanopore 110) modulates/changes the baselinetransistor current (which is measured when no base/molecule is in thenanopore 110) by the example current change amount (for the timeduration) shown in graph 600. When present in the nanopore 110, thismodulation/change (including the shape and other characteristics of thetransistor current pulse) in transistor current (measured by the ammeter220) is used by the software application 1060 to determine the type ofbase 218 from the other bases 218 of the DNA module 217 and/or todetermine the type of biomolecule from the other biomolecules.

FIG. 4 shows a setup 400 of the graphene nanopore transistor device 100for biomolecule sensing according to an embodiment. FIG. 4 shows across-sectional view of the graphene nanopore transistor device 100. Theelements in FIG. 4 are the same as described FIGS. 1 and 3. In FIG. 4,however, biomolecules 221-224, such as protein, DNA, RNA, etc., havebeen loaded into the graphene nanopore transistor device 100. When thebiomolecules 221-224 are individually driven through the nanopore 110via either fluidic pressure bias between the two sides (of the tworeservoirs 211 and 212) of the graphene nanopore transistor device 100(chip) (when the biomolecules 221-224 are uncharged), voltage biasapplied by voltage source 216 (when the biomolecules 221-224 arecharged) or both, at least two parameters can be extracted: (1) ioniccurrent as measured by ammeter 225, depending on the size of themolecule/biomolecule in the nanopore 110; and (2) modulation of thegraphene transistor current measured by the ammeter 220, which dependson the total surface charge of the biomolecule 221-224 in the nanopore110 (as discussed in FIG. 6). As one embodiment for data analysis, by(the software application 1060 on the computer 1000) plotting these twoparameters in a scatter plot, one (the software application 1060) willbe able to differentiate and identify each type of the biomolecules221-224. As discussed above in FIG. 6, each respective biomolecule221-224 in the nanopore 110 (one at a time) modulates the baselinecurrent (which is measured when no base/biomolecule is in the nanopore110) by the current change amount as shown in graph 600. This modulation(change) in transistor current (measured by the ammeter 220) is used bythe software application 1060 to determine the type of biomolecule(e.g., biomolecule 224 presently in the nanopore 110) from the otherbiomolecules 221, 222, 223 in the reservoir 211.

Additionally, the ionic current (measured by ammeter 225 for thebaseline ionic current when no base/molecule is in the nanopore 110)flows from electrochemical electrode 215 to the conductive ionic buffer213 in the upper chamber (i.e., top reservoir 211), then to the nanopore110, then to the ionic buffer 213 in the bottom chamber (i.e., bottomreservoir 212), and then to electrochemical electrode 214.

When a biomolecule (such as biomolecule 221, 222, 223, and/or 224) is inthe nanopore 110, the biomolecule affects (modulates) the (baseline)ionic current. The ionic current (measured by ammeter 225 when a base218 and/or biomolecule 221-224 is individually in the nanopore 110)flows from electrochemical electrode 215 to the conductive ionic buffer213 in the upper chamber (i.e., top reservoir 211), then to the nanopore110 where, e.g., the biomolecule 224 changes the flow of ionic current,then to the ionic buffer 213 in the bottom chamber (i.e., bottomreservoir 212), and then to electrochemical electrode 214.

The ionic current (when voltage is applied by voltage source 216) asmeasured by ammeter 225 is modulated depending on the size of themolecule/biomolecule in the nanopore 110 as shown in FIG. 7, where alarger size changes to ionic current more than a smaller sizemolecule/biomolecule. The graph 700 shows the magnitude/amplitude (e.g.,in nanoamps) of the ionic current pulse height (relative to the baselinelevel when there is no DNA (base 218) and/or molecules (e.g.,biomolecule 221, 222, 223, 224) inside the nanopore) on the y-axis andshows the time duration (t) of the ionic current pulse on the x-axis.For each respective biomolecule 221, 222, 223, 224 (and/or eachrespective base 218), a corresponding ionic current trace (of its ioniccurrent pulse measured when inside the nanopore 110) is graphed with atime duration (t) and magnitude as seen in FIG. 7. For example, theindividual biomolecule 221-224 (and/or base 218) in the nanopore 110modulates the baseline current (which is measured when no base/moleculeis in the nanopore 110) by the example current change amount shown ingraph 700. This modulation (change) in ionic current (measured by theammeter 225) is used by the software application 1060 to determine thetype of biomolecule from the other biomolecules 221-224 (and/ordetermine the type of base 218 from the other bases 218 of the DNAmodule 217).

Accordingly, a biomolecule can be identified/sequenced by the magnitudeof its ionic current pulse due to its presence inside the nanopore andthe time duration of its ionic current pulse (the time it takes the DNAbase to pass through the nanopore) as expected for a given biomoleculeof the same type.

FIG. 5 shows a setup 500 of the graphene nanopore transistor device 100for biomolecule sensing according to an embodiment. FIG. 5 shows across-sectional view of the graphene nanopore transistor device 100. Theelements in FIG. 5 are the same as described in FIGS. 1, 3, and 4. InFIG. 5, however, the setup 500 shows that the nanopore 110 can also becoated with an organic coating/layer 226, which can differentiallyinteract with each type of biomolecules 221-224 (and/or base 218), e.g.,forming transient chemical bonds 227, etc. In this way, a thirdparameter (in addition to the first and second parameters) can beextracted, and the third parameter is the time (i.e., duration time) ittakes for the molecule 221-224 to pass through the nanopore 110, whichcan be measured from the pulse time duration of the current signal from(either) the ionic current measured by ammeter 225 and/or transistorcurrent measured by ammeter 220.

Further regarding the organic coating 226, the organic coating 226 isapplied to the nanopore 110 on the insulation layer 106, the graphenelayer 104, and the insulation layer 102. The organic coating 226 has oneend bonded to the inner surface of (layers 106, 104, 102 inside) thenanopore 110 and the other end (functional group) is free in thenanopore 110 to interact with biomolecules 221-224 and/or DNA bases 218of a molecule. The other free end (functional group) of the organiccoating 226 forms transient bonds to the bases of molecules and/or tobiomolecules as discussed herein. The transient bonds 227 of the organiccoating 226 keep the biomolecules and/or DNA molecule from moving whilein the nanopore 110. A voltage bias (by the voltage source 216) can beapplied to break the transient bonds and then move the biomoleculesand/or DNA molecule through the nanopore 110 as desired.

Further, information regarding the organic coating can be found inapplication Ser. No. 13/359,743, filed Jan. 27, 2012, entitled “DNAMOTION CONTROL BASED ON NANOPORE WITH ORGANIC COATING FORMING TRANSIENTBONDING TO DNA” and application Ser. No. 13/359,729, filed Jan. 27,2012, entitled “ELECTRON BEAM SCULPTING OF TUNNELING JUNCTION FORNANOPORE DNA SEQUENCING” which are herein incorporated by reference intheir entirety.

The strength of the transient bonds 227 to each respective biomolecule221, 222, 223, 224 is different based on the type of biomolecule that ispresently in the nanopore 110. As such, the time duration (plot of timeversus magnitude as seen in graph 700 on, e.g., a display of thecomputer 1000 operatively connected to the ammeter 225 and/or voltagesource 216 as understood by one skilled in the art) of the measuredionic current (by ammeter 225) will be longer in time for thebiomolecule (e.g., biomolecule 224) having a stronger transient bond 227to the organic coating 226. The time duration in the nanopore 110 isbased on the combination of the transient bond 227 plus the respectivecharge of the particular biomolecule 221, 222, 223, 224. As such, forthe same transient bond 227, a biomolecule with less charge stays in thenanopore 110 for a longer time duration than a biomolecule with morecharge, thus requiring a larger amount of voltage to drive theless-charged biomolecule out of the nanopore 110.

There are many choices for the organic coating 226, and the organiccoating 226 can be chosen to have a special interaction (i.e., a strongtransient bond) to certain types of biomolecules which will increase thetime duration of the ionic current for that particular biomolecule, andincrease the detection of that particular biomolecule. Examples pairs ofthe biomolecule and organic coating 226 that form a strong bond includebut are not limited to an antigen (biomolecule) and an antibody (organiccoating) pair, DNA base (biomolecules) and its complementary DNA base(organic coating) pair, hydrophobic molecules and hydrophobic coatingpairs, hydrophilic molecules and hydrophilic coating pair, etc.

DNA base A bonds with T while base C bonds with G. In other words, BaseA and T are complementary bases for each other, while base C and G arecomplementary bases for each other.

In chemical-physics, hydrophobicity is the physical property of amolecule (known as a hydrophobe) that is repelled from a mass of water.Hydrophobic molecules tend to be non-polar and, thus, prefer otherneutral molecules and non-polar solvents. Hydrophobic molecules in wateroften cluster together, forming micelles. Examples of hydrophobicmolecules include the alkanes, oils, fats, and greasy substances ingeneral. Hydrophobic materials are used for oil removal from water, themanagement of oil spills, and chemical separation processes to removenon-polar from polar compounds. On the other side, a hydrophile is amolecule or other molecular entity that is attracted to, and tends to bedissolved by, water. A hydrophilic molecule or portion of a molecule isone that has a tendency to interact with or be dissolved by water andother polar substances. Hydrophilic substances can seem to attract waterout of the air, the way salts (which are hydrophilic) do. Sugar, too, ishydrophilic, and like salt is sometimes used to draw water out of foods.There are hydrophilic and hydrophobic parts of the cell membrane. Ahydrophilic molecule or portion of a molecule is one that is typicallycharge-polarized and capable of hydrogen bonding, enabling it todissolve more readily in water than in oil or other hydrophobicsolvents. Hydrophilic and hydrophobic molecules are also known as polarmolecules and nonpolar molecules, respectively. Some hydrophilicsubstances do not dissolve. This type of mixture is called a colloid.Soap, which is amphipathic, has a hydrophilic head and a hydrophobictail, allowing it to dissolve in both waters and oils.

FIG. 8 is a flow chart of a method 800 for electrically differentiatingbases 218 of the DNA molecule 217 and/or identifying biomolecules221-224 according to an embodiment.

At block 805, a reservoir (top and bottom reservoirs 211 and 212) isseparated into two parts by a membrane (e.g., layers 102,104, 106). Ananopore 110 is formed through the membrane, and the nanopore 110connects the two parts of the reservoir at block 810. The nanopore 110and the two parts of the reservoir are filled with ionic buffer 213 atblock 815. The membrane comprises a graphene layer 104 and insulatinglayers 102 and 106. At block 820, the graphene layer 104 is wired tofirst and second metal pads (e.g., metal pads 105 a and 105 b via holes107 and 108 respectively) to form a graphene nanopore transistor 100 inwhich transistor current flowing through the graphene nanoporetransistor 100 is modulated by charges (of the base 218 and/orbiomolecules 221-224 respectively) passing through the nanopore 110.

The charges correspond to a base 218 of the molecule 217. When the base218 is in the nanopore 110, the transistor current modulates based onthe charges or dipole moment of the base 218 to form a transistorcurrent pulse (e.g., as shown in FIG. 6). The base 218 isdetermined/differentiated (i.e., sequenced) based on a magnitude, a timeduration, and/or a shape of the transistor current pulse when theparticular base 218 is in the nanopore 110.

The charges correspond to a biomolecule (such as biomolecules 221-224).When the particular biomolecule (e.g., biomolecule 224) is in thenanopore 110, the transistor current modulates based on the charges ordipole of that particular biomolecule 224 to form a transistor currentpulse (e.g., as shown in FIG. 6). The particular biomolecule 224 isdetermined/differentiated based on a magnitude and a time duration ofthe transistor current pulse when the biomolecule 224 is in the nanopore110.

When a voltage (by voltage source 216) is applied across the nanopore110, an ionic current is changed based on a size of the biomolecule(e.g., biomolecule 224) to form an ionic current pulse, and thebiomolecule 224 is determined based on a magnitude and a time durationof the ionic current pulse when the biomolecule is in the nanopore 110(e.g., as shown in FIG. 7).

FIG. 9 is a flow chart of a method 900 for electrically differentiatingbases 218 of the DNA molecule 217 and/or identifying biomolecules221-224 according to an embodiment.

At block 905, a reservoir (top and bottom reservoirs 211 and 212) isseparated into two parts by a membrane (e.g., layers 102,105, 106). Ananopore 110 is formed through the membrane, and the nanopore 110connects the two parts of the reservoir at block 910. The nanopore 110and the two parts of the reservoir are filled with ionic buffer 213 atblock 915. The membrane comprises a graphene layer 104 and insulatinglayers 102 and 106.

The graphene layer 104 is wired to first and second metal pads (e.g.,metal pads 105 a and 105 b via holes 107 and 108 respectively) to form agraphene nanopore transistor 100 in which transistor current flowingthrough the graphene nanopore transistor 100 is modulated by chargespassing through the nanopore 110, where the charges correspond to atleast one of a base 218 and/or a biomolecule 221-224 at block 920. Todistinguish an individual base 218 and/or an individual biomolecule(e.g., biomolecule 224), the nanopore 110 is coated with an organiccoating/layer 226 configured to at least one of interact with theparticular type of base 218 differently (e.g., form a stronger bond)than other types of bases 218 and/or interact with the particularbiomolecule (e.g., biomolecule 224) differently (e.g., form a strongerbond) than other biomolecules 221-223 at block 925.

When the charges or dipoles correspond to the base 218 of a molecule 217and when the base 218 is in the nanopore 110, the transistor currentmodulates based on the charges or dipoles of the base 218 to form atransistor current pulse (e.g., shown in FIG. 6). As such, the base 218is determined based on a magnitude, a time duration, and/or a shape ofthe transistor current pulse when the base 218 is in the nanopore 110.

When the charges or dipoles correspond to the biomolecule (e.g.,biomolecule 224) and when the biomolecule is in the nanopore 110, thetransistor current modulates based on the charges or dipoles of thebiomolecule to form a transistor current pulse (e.g., as shown in FIG.6). As such, the biomolecule is determined based on a magnitude and atime duration of the transistor current pulse when the biomolecule is inthe nanopore 110.

When a voltage is applied (by the voltage source 216) across thenanopore 110, an ionic current is changed based on a size of thebiomolecule 221-224 to form an ionic current pulse (e.g., as shown inFIG. 7). As such, the biomolecule is determined/differentiated based ona magnitude and a time duration of the ionic current pulse when thebiomolecule (e.g., biomolecule 224) is in the nanopore 110.

When the molecule 217 is a DNA molecule, the bases 218 respectivelycomprise at least one of adenine, guanine, thymine, and cytosine. Whenthe molecule 217 is an RNA molecule, the bases 218 respectively compriseat least one of adenine, cytosine, guanine, uracil, thymine,pseudouridine, methylated cytosine, and guanine.

FIG. 10 illustrates an example of a computer 1000 (e.g., as part of thecomputer setup for testing and analysis) having capabilities, which maybe included in exemplary embodiments. Various methods, procedures,modules, flow diagrams, tools, applications, circuits, elements, andtechniques discussed herein may also incorporate and/or utilize thecapabilities of the computer 1000. Moreover, capabilities of thecomputer 1000 may be utilized to implement features of exemplaryembodiments discussed herein. One or more of the capabilities of thecomputer 1000 may be utilized to implement, to connect to, and/or tosupport any element discussed herein (as understood by one skilled inthe art) in FIGS. 1-9. For example, the computer 1000 which may be anytype of computing device and/or test equipment (including ammeters,voltage sources, connectors, etc.). Input/output device 1070 (havingproper software and hardware) of computer 1000 may include and/or becoupled to the nanodevices discussed herein via cables, plugs, wires,electrodes, etc. Also, the communication interface of the input/outputdevices 1070 comprises hardware and software for communicating with,operatively connecting to, reading, and/or controlling voltage sources,ammeters, and ionic current traces (e.g., magnitude and time duration ofionic current and or transistor current), etc., as discussed herein. Theuser interfaces of the input/output device 1070 may include, e.g., atrack ball, mouse, pointing device, keyboard, touch screen, etc., forinteracting with the computer 1000, such as inputting information,making selections, independently controlling different voltages sources,and/or displaying, viewing and recording ionic current traces for eachbase, molecule, biomolecules, etc.

Generally, in terms of hardware architecture, the computer 1000 mayinclude one or more processors 1010, computer readable storage memory1020, and one or more input and/or output (I/O) devices 1070 that arecommunicatively coupled via a local interface (not shown). The localinterface can be, for example but not limited to, one or more buses orother wired or wireless connections, as is known in the art. The localinterface may have additional elements, such as controllers, buffers(caches), drivers, repeaters, and receivers, to enable communications.Further, the local interface may include address, control, and/or dataconnections to enable appropriate communications among theaforementioned components.

The processor 1010 is a hardware device for executing software that canbe stored in the memory 1020. The processor 1010 can be virtually anycustom made or commercially available processor, a central processingunit (CPU), a data signal processor (DSP), or an auxiliary processoramong several processors associated with the computer 1000, and theprocessor 1010 may be a semiconductor based microprocessor (in the formof a microchip) or a macroprocessor.

The computer readable memory 1020 can include any one or combination ofvolatile memory elements (e.g., random access memory (RAM), such asdynamic random access memory (DRAM), static random access memory (SRAM),etc.) and nonvolatile memory elements (e.g., ROM, erasable programmableread only memory (EPROM), electronically erasable programmable read onlymemory (EEPROM), programmable read only memory (PROM), tape, compactdisc read only memory (CD-ROM), disk, diskette, cartridge, cassette orthe like, etc.). Moreover, the memory 1020 may incorporate electronic,magnetic, optical, and/or other types of storage media. Note that thememory 1020 can have a distributed architecture, where variouscomponents are situated remote from one another, but can be accessed bythe processor 1010.

The software in the computer readable memory 1020 may include one ormore separate programs, each of which comprises an ordered listing ofexecutable instructions for implementing logical functions. The softwarein the memory 1020 includes a suitable operating system (O/S) 1050,compiler 1040, source code 1030, and one or more applications 1060 ofthe exemplary embodiments. As illustrated, the application 1060comprises numerous functional components for implementing the features,processes, methods, functions, and operations of the exemplaryembodiments. The application 1060 of the computer 1000 may representnumerous applications, agents, software components, modules, interfaces,controllers, etc., as discussed herein but the application 1060 is notmeant to be a limitation.

The operating system 1050 may control the execution of other computerprograms, and provides scheduling, input-output control, file and datamanagement, memory management, and communication control and relatedservices.

The application 1060 may be a source program, executable program (objectcode), script, or any other entity comprising a set of instructions tobe performed. When a source program, then the program is usuallytranslated via a compiler (such as the compiler 1040), assembler,interpreter, or the like, which may or may not be included within thememory 1020, so as to operate properly in connection with the O/S 1050.Furthermore, the application 1060 can be written as (a) an objectoriented programming language, which has classes of data and methods, or(b) a procedure programming language, which has routines, subroutines,and/or functions.

The I/O devices 1070 may include input devices (or peripherals) such as,for example but not limited to, a mouse, keyboard, scanner, microphone,camera, etc. Furthermore, the I/O devices 1070 may also include outputdevices (or peripherals), for example but not limited to, a printer,display, etc. Finally, the I/O devices 1070 may further include devicesthat communicate both inputs and outputs, for instance but not limitedto, a NIC or modulator/demodulator (for accessing remote devices, otherfiles, devices, systems, or a network), a radio frequency (RF) or othertransceiver, a telephonic interface, a bridge, a router, etc. The I/Odevices 1070 also include components for communicating over variousnetworks, such as the Internet or an intranet. The I/O devices 1070 maybe connected to and/or communicate with the processor 1010 utilizingBluetooth connections and cables (via, e.g., Universal Serial Bus (USB)ports, serial ports, parallel ports, FireWire, HDMI (High-DefinitionMultimedia Interface), etc.).

When the computer 1000 is in operation, the processor 1010 is configuredto execute software stored within the memory 1020, to communicate datato and from the memory 1020, and to generally control operations of thecomputer 1000 pursuant to the software. The application 1060 and the O/S1050 are read, in whole or in part, by the processor 1010, perhapsbuffered within the processor 1010, and then executed.

When the application 1060 is implemented in software it should be notedthat the application 1060 can be stored on virtually any computerreadable storage medium for use by or in connection with any computerrelated system or method. In the context of this document, a computerreadable storage medium may be an electronic, magnetic, optical, orother physical device or means that can contain or store a computerprogram for use by or in connection with a computer related system ormethod.

The application 1060 can be embodied in any computer-readable medium1020 for use by or in connection with an instruction execution system,apparatus, server, or device, such as a computer-based system,processor-containing system, or other system that can fetch theinstructions from the instruction execution system, apparatus, or deviceand execute the instructions. In the context of this document, a“computer-readable storage medium” can be any means that can store,read, write, communicate, or transport the program for use by or inconnection with the instruction execution system, apparatus, or device.The computer readable medium can be, for example but not limited to, anelectronic, magnetic, optical, or semiconductor system, apparatus, ordevice.

More specific examples (a nonexhaustive list) of the computer-readablemedium 1020 would include the following: an electrical connection(electronic) having one or more wires, a portable computer diskette(magnetic or optical), a random access memory (RAM) (electronic), aread-only memory (ROM) (electronic), an erasable programmable read-onlymemory (EPROM, EEPROM, or Flash memory) (electronic), an optical fiber(optical), and a portable compact disc memory (CDROM, CD R/W) (optical).

In exemplary embodiments, where the application 1060 is implemented inhardware, the application 1060 can be implemented with any one or acombination of the following technologies, which are each well known inthe art: a discrete logic circuit(s) having logic gates for implementinglogic functions upon data signals, an application specific integratedcircuit (ASIC) having appropriate combinational logic gates, aprogrammable gate array(s) (PGA), a field programmable gate array(FPGA), etc.

It is understood that the computer 1000 includes non-limiting examplesof software and hardware components that may be included in variousdevices, servers, and systems discussed herein, and it is understoodthat additional software and hardware components may be included in thevarious devices and systems discussed in exemplary embodiments.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described above with reference toflowchart illustrations and/or schematic diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

As described above, embodiments can be embodied in the form ofcomputer-implemented processes and apparatuses for practicing thoseprocesses. In embodiments, the invention is embodied in computer programcode executed by one or more network elements. Embodiments include acomputer program product on a computer usable medium with computerprogram code logic containing instructions embodied in tangible media asan article of manufacture. Exemplary articles of manufacture forcomputer usable medium may include floppy diskettes, CD-ROMs, harddrives, universal serial bus (USB) flash drives, or any othercomputer-readable storage medium, wherein, when the computer programcode logic is loaded into and executed by a computer, the computerbecomes an apparatus for practicing the invention. Embodiments includecomputer program code logic, for example, whether stored in a storagemedium, loaded into and/or executed by a computer, or transmitted oversome transmission medium, such as over electrical wiring or cabling,through fiber optics, or via electromagnetic radiation, wherein, whenthe computer program code logic is loaded into and executed by acomputer, the computer becomes an apparatus for practicing theinvention. When implemented on a general-purpose microprocessor, thecomputer program code logic segments configure the microprocessor tocreate specific logic circuits.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

What is claimed is:
 1. A method for electrically differentiating bases,the method comprising: providing a reservoir structure separated intotwo parts by a membrane, wherein a nanopore is formed through themembrane, wherein the membrane comprises a graphene layer and insulatinglayers, wherein the graphene layer is coupled to first and second metalpads to form a graphene transistor, wherein the first metal pad forms astep on one of the insulating layers such that a bottom surface of thefirst metal pad is directly on top of the graphene layer and the bottomsurface is directly on top of the one of the insulating layers, whileanother one of the insulating layers is directly on top of the firstmetal pad, wherein the step of the first metal pad is external to thereservoir structure; and using transistor current flowing through thegraphene transistor to differentiate bases, the transistor current beingmodulated by charges or dipoles passing through the nanopore.
 2. Themethod of claim 1, wherein the nanopore connects the two parts of thereservoir structure.
 3. The method of claim 1, wherein the first andsecond metal pads include titanium.
 4. The method of claim 1, whereinthe first and second metal pads include palladium.
 5. The method ofclaim 1, wherein the first and second metal pads include gold.
 6. Themethod of claim 1, where the insulating layers include oxide.
 7. Themethod of claim 1, where the insulating layers include nitride.
 8. Themethod of claim 1, wherein the charges or dipoles correspond to anucleobase of a nucleic acid molecule.
 9. The method of claim 8, whereinwhen the nucleobase is in the nanopore, the transistor current modulatesbased on the charges or dipoles of the nucleobase to form a transistorcurrent pulse.
 10. The method of claim 9, further comprising determiningthe nucleobase based on at least one of a magnitude, a time duration,and a shape of the transistor current pulse when the nucleobase is inthe nanopore.
 11. The method of claim 1, wherein the charges or dipolescorrespond to a biomolecule.
 12. The method of claim 11, wherein whenthe biomolecule is in the nanopore, the transistor current modulatesbased on the charges or dipoles of the biomolecule to form a transistorcurrent pulse.
 13. The method of claim 12, further comprisingdetermining the biomolecule based on at least one of a magnitude, a timeduration, and a shape of the transistor current pulse when thebiomolecule is in the nanopore.
 14. The method of claim 12, wherein whena voltage is applied across the nanopore, an ionic current is changedbased on a size of the biomolecule to form an ionic current pulse. 15.The method of claim 14, wherein the biomolecule is determined based on amagnitude and a time duration of the ionic current pulse when thebiomolecule is in the nanopore.
 16. The method of claim 1, wherein thereservoir structure includes ionic buffer.
 17. The method of claim 1,wherein the nanopore is configured to pass a protein.
 18. The method ofclaim 1, wherein the nanopore is configured to pass DNA.
 19. The methodof claim 1, wherein the nanopore is configured to pass RNA.
 20. Themethod of claim 1, wherein the reservoir structure comprises a top partand a bottom part.